File creation . CRM and delimiter insertion (HEXA 0D0A) after certain information block

Question

I am creating a PHP text file that is saved with the . CRM extension, used for database collection files. The file, in its structure, has 3 parts: HEADER, DETAIL and TRAILER. Each one has 400 exact characters in the file. At the end of each of these parts, I must, according to the documentation, insert:

"At the end of the file, that is, after the information Header, Detail and Trailer there should be the Tape Mark or file finalizer that is also known in the encoding as delimiter (HEXA 0D0A). It’s as if after the last 400 column of the Trailer was given a ENTER to go to the next row."

Someone who can help me insert this delimiter? If I open the file and count the characters, I have a total of 1202 (400 from the header, 400 from the detail, 400 from the trailer and 2 are line breaking between header-detail and detail-trailer). This line break needs to be deleted (replace with delimiter) so that the file has 1200 characters.